1. Field of the Invention
The present invention relates to viral inhibitors that prevent the replication of hepatitis C virus by inhibiting host factors involved in the replication of hepatitis C virus, BGT-1 and/or AKR1.
2. Background Art
Hepatitis C virus (HCV) is the major causal agent of post-transfusion non-A, non-B hepatitis and the hepatitis caused by this virus is often chronic. The cDNA of this virus was cloned in 1989 by Choo et al. (Choo, Q. L. et al., Science, 244, 359-362, 1989), and the virus is known as a single-stranded RNA virus belonging to the Flavivirus family (Kato, N. et al., Proc. Natl. Acad. Sci. USA, 87, 9524-9528, 1990). The complete nucleotide sequence and corresponding amino acid sequence were explained by several groups. We previously prepared a vector that expresses the full-length HCV gene (WO99/67394).
There is an urgent need to discover a therapeutic means for hepatitis C, partially because any medicine showing a complete anti-viral effect has not been established. Currently, the most effective treatment is a combination therapy with pegylated interferon and Ribavirin. However, a complete response to even this therapy is achieved in only about 50% of patients infected with HCV genotype 1b for which many antibody-positive patients exist in Japan and interferon is less effective, and it would be highly desirable to develop a new antiviral agent. It is said that 170,000,000 HCV-positive patients exist in the world including 2,000,000 or more patients in Japan and the progression of hepatitis C to liver cancer or cirrhosis occurs at high probability so that a therapeutic means must be urgently established. Attempts were previously made to develop antiviral drugs based on the inhibition of the protease activity of nonstructural proteins involved in the replication of HCV (NS3, NS5) or the like, but any sufficient effect has not been achieved due to a large number of mutations in the virus gene and other reasons.
Among four subtypes of the inhibitory neurotransmitter GABA transporter, only BGT-1 (betaine/GABA transporter 1) has affinity for betaine. Betaine is one of substances called compatible solutes, which are synthesized to restore osmotic balance between the inside and outside of a cell and narrowly refers to trimethylglycine. In 1992, it was cloned from MDCK cells derived from dog kidney (Yamauchi et al., J. Biol. Chem. 267, 649-652, 1992). BGT-1 is peripherally expressed mainly in kidney and liver, and occurs in astroglia in the cerebellum, cerebral cortex, brain stem and the like in the central nervous system. However, BGT-1 is not always expressed near GABAergic neurons, suggesting that BGT-1 is more likely to be involved in the removal of GABA escaping from the synapse or osmoregulation rather than the termination of neurotransmission of GABAergic neurons. Any relation to HCV has not been reported.
AKR1C1 (Aldo-Keto Reductase Family 1) functions to convert an aldehyde or a ketone into an alcohol by utilizing NADH or NADPH and exists as a monomer (around 35 kDa) in the cytoplasm. It is highly expressed in liver along with AKR1C4 (Steckelbroeck, S. et al., J. Pharm. Exp. Ther. 316, 1300-1309, 2006). It is reported to be absent in breast cancer or the like (Ji, Q et al., Cancer Research 64, 7610-7617, 2004). It is also reported that the expression of AKR1C1 was decreased by a nonstructural protein of HCV, NS4B (Zheng, Y et al., J. Biochem. Mol. Biol. 38, 151-160, 2005).
Recently, a method for inhibiting the expression of a specific gene in a cell in an animal body was found, which comprises inhibiting the expression of the target gene using a double-stranded RNA against the target gene (Fire A et al., Nature 391:806-811 (1998)). This method is called RNA interference (RNAi), and based on the phenomenon that when a double-stranded RNA (dsRNA) is introduced into a cell, an mRNA corresponding to the RNA sequence in the cell is specifically degraded and no more expressed as a protein. RNAi is an effective method for studying the functions of novel genes by inhibiting their expression and extensively used for gene function analysis of nematodes, drosophilas, etc. However, it has been unknown whether or not RNAi is effective for the treatment of diseases, especially viral diseases such as hepatitis C.